The chemical, sediment and total load carried by the major river basins in India—Ganges, Brahmaputra, Indus (Jhelum), Godavari, Krishna, Narmada, Tapti, Mahnadi and Cauvery have been calculated, based partly on new set of data and partly on existing data. There is a significant amount of chemical load transported by all the Indian rivers, and for global mass transfer calculation, these cannot and should not be ignored. The chemical mass transfer during the monsoon is not surprisingly small, as would be expected for excess discharge and dilution controlled run-off. The sediment mass transfer from non-Himalyan rivers, all within the same range of magnitude, accounts for less than a tenth of that of the Ganges but during the monsoon, except for Cauvery, all the Indian rivers carry a sediment load of greater than 1000 ppm. The total mass transfer from the Indian subcontinent accounts for 6·5 per cent of the global transfer.

Except for the Ganges and the Brahmaputra, the erosion rates are similar for all Indian basins, independent of their size and these rates are agreeable with the continental earth average. The Ganges-Brahmaputra basin erosion rates are highest on the continental earth. Based on the average rate of denudation of the Indian subcontinent, the mean elevation of this landmass will be that of the present day mean sea level in 5 million years from now. The average denudation rate of 2·1 cm/100 years is different from the calculated average sedimentation rate of 2·1 cm/100 years is different from the calculated average sedimentation rate of 6·7 cm/100 years in the Bay of Bengal suggesting that an accurate erosion rate in the continent is needed to determine sedimentation rate in the oceans.

The chemical and sediment mass transfer rates appear to have a logarithmic linear relationship on a global scale, as against the reported negative logarithmic trend for North America alone.

Three vertical magnetic profiles were run across an iron-ore formation near Addatigala. Theoretical fits have been obtained for the observed anomaly curves and the possible relation between the formation of the structure and eastern ghat tectonics is discussed. Laboratory determination of the susceptibility, remanence and coercivity of two samples from the structure have been made at various field strengths and the results are discussed.

Boron content has been determined in the acid insoluble fraction of the carbonate rocks of the Kajrahat formation. Their comparison with the boron content of the shales of known environment suggests brackish to marine salinity levels during deposition. The dolomites register higher salinity conditions than the limestones. The salinity of the basin may have changed at intervals.

The Kaladgi argillites show heterogeneity in textural and physical properties. Differential thermal analysis and thermogravimetric studies have revealed that the argillites contain illite with montmorillonite, quartz and biotite. The calc-rich shale contains illite and kaolinite with total absence of montmorillonite. The mineralogical significance of the depositional environment of the Kaladgi (precambrian) sea has been discussed.

Geomagnetic disturbance effects on the occurrence of range and frequency spread at Huancayo are studied for the period 1957–74. The occurrence of frequency spread is decreased on disturbed days forD-months andE-months while duringJ-months an increase is noted in the post-midnight period. The occurrence of range spread is decreased on disturbed days in the pre-midnight hours duringD andE-months. Post-midnight hours ofD andE-months and all hours of night duringJ-months show an increase of range spread on disturbed days, which is most prominent during low sunspot years. The mean occurrence of frequency spread (2300–0100 LT) and range spread (2000–2300 LT) decrease with increasing ΣKp. On the other hand, occurrence of range spread (0300–0500 LT) increases with increasing ΣKp, and is suggested as the consequence of the changes of the horizontal electric field in theF-region associated with the geomagnetic storms.

The post-sunset maximum in virtual height of theF region near the magnetic equator is associated with the general rise of the wholeF region from the base to the height of peak ionisation with little change in the semi-thickness of the layer. This rise ofF region is accentuated on days with large evening peak in the vertical drift velocity or the horizontal electric field in theF region. The range type of equatorial spreadF first occurs only if theF region drift velocity remains significantly upwards after sunset but the maximum intensity of spreadF occurs when the drift velocities are low or even downwards. The range spread first appears at or below the base of theF layer and later spreads into theF layer due to downward movement of the layer and/or upward movement of the irregularity. SpreadF seen on VHF backscatter records corresponds to the range type of spreadF seen on normal ionograms. The frequency type of spreadF does not produce VHF echoes. A strong peak in the electric field seems to be a necessary condition for the generation of equatorial spreadF.

An examination of day-to-day and monthly mean positions of the electrojet axis in relation to the changes in the apparent solar declination, in the Indian equatorial region shows marked association between the two. For relatively quiet days, significant correlations are observed between the solar declination and each of the parameters, the northernSq focal latitude, the jet axis and the line of maximumSq(H). From the significant mutual association of these parameters, it has been suggested that the equatorial electrojet could be a part of the world-wideSq current system.

The signature of the interplanetary magnetic field componentBy andBz and their effects on the low lattitude field are studied for Alibag station. It has been found that the direction and magnitude of theBy component of IMF have their signatures on the low latitude geomagnetic field, varying with the time of the day and season.

The total electron content data obtained at Ahmedabad through the Faraday fading records of the radio beacons abroad the satellites Explorer 22 and 27 are used to determine the overhead integrated production rate (Q0) and integrated loss coefficient (β′) for the epoch 1965–1968. The production rate (Q0) is shown to have two peaks during a year around the equinoctal months and for a particular monthQ0 increases linearly with the 10·7 cm solar flux. The loss coefficient β′, too, has two equinoctial peaks within a year. The semiannual variations ofQ0 and β′ are discussed in relation to similar variation in the [O]/[N2] ratio.

Detectable ionization effects in the ionosphericD-region from individual, strong and steady x-ray sources such as Sco X-1 and transient x-ray sources such as Cet X-2 have been reported by us and many others previously based on the field strength and phase variations of the VLF data. As a follow up to these investigations, we have examined the integrated effects of many of the known x-ray sources discovered by UHURU, ANS, Ariel V and SAS-3 satellites, in order to understand the totality of their effects. These effects are examined in the present paper for 0° and +38° geographic latitudes corresponding to midnight conditions and for different times of the year. Such effects are compared, in turn, with those of the known steady sources responsible forD-region ionization such as Lyman-alpha and galactic cosmic radiations. The results are presented as profiles of electron production rates as a function of height. Our study leads to the conclusion that there should be detectable annual variations of the electron density which are pronounced around May-August. Further, the results of the computations on electron production rates corresponding to the spectacular x-ray nova A0620-00 are also included in the present paper.

A new model of a Gaussian ionospheric irregularity with perturbation is studied. Analysis of two events of diffraction of ATS-6 radio signals on 40, 140 and 360 MHz by isolated ionospheric irregularities indicates that while one class of events is well described in terms of diffraction by a Gaussian irregularity, the other class of events necessitates the assumption of a more complex irregularity structure.

General characteristics of diffraction patterns due to a minor Gaussian perturbation within a larger irregularity are discussed, and an attempt has been made to deduce the structure of the second observed irregularity on the basis of these characteristics. The result suggests the possibility of a distorted double-humped electron density distribution in the irregularity.

Simultaneous observations of amplitude scintillations at 40 MHz, 140 MHz and 360 MHz radiated from ATS-6 satellite at 34° E longitude were made at Ootacamund near the magnetic equator in India. It has been found that the frequency variation of scintillation index (S4) isS4 ∞f−n, withn being about 1·2 only for weak scintillations, i.e., so long as the scintillation index does not exceed 0·6 at the lower frequency. For strong scintillations (S4&gt;0·6) where multiple scattering may be present, the exponentn itself is a function of the intensity of scintillation, the scintillation indices at two frequencies are related by:S4(f1)=S4(f2) exp [1·3 log(f2/f1)(1−S4(f2)] so long asf2/f1≤3. Thus knowing scintillation index at a given frequency one can estimate the scintillation index at another frequency. This will be of significant importance for communication problems. Evidence is also shown for the reversal of the frequency law in cases of intense scintillations.